The director of the Federal Bureau of Investigation says his agency has transformed itself, and he does not believe the mistakes that led to the September 11 attacks on the United States would happen again.

FBI Director Robert Mueller told a House of Representatives subcommittee Tuesday that since September 11, 2001, his agency's number one priority has been preventing terrorist attacks against the United States. He said the lack of information sharing within the FBI and with other agencies, which some say is to blame for the failure to not stop the attacks, is a thing of the past.

"I believe that what one saw happen in the days and weeks before September 11th would not happen again," said Robert Mueller. "That is not to say that we could not face another terrorist attack, but I believe we are far more efficient and effective, not only the FBI itself, but also the FBI in conjunction with the Department of Homeland Security, the CIA [Central Intelligence Agency], DIA [Defense Intelligence Agency], NSA [National Security Administration] and all those who play a role in protecting the public."

Director Mueller was responding to questions about the trial of admitted al-Qaida operative Zacarias Moussaoui. Moussaoui faces the death penalty in a U.S. court for his role in the September 11 attacks. Prosecutors charge that he lied about his al-Qaida membership and did not give authorities information about the planned attacks when federal agents arrested him weeks before they happened.

Mueller was on Capitol Hill to discuss the agency's 2007 budget request of $6 billion, which he said would go to support more than 31,000 jobs, as well as new technology and expanded facilities for the Bureau. He also answered lawmakers' questions about other national security issues.

He said China has a major spying program directed against the United States, which he called a "substantial threat."

The director also said the FBI is closely watching the case of former Liberian president and war crimes suspect Charles Taylor. The United States has expressed deep concern over reports that the former leader has disappeared from his Nigerian place of exile.

"We are monitoring what is happening in conjunction with the State Department, and to the extent that we are asked to provide any assistance in whatever way, we will," he said.

Director Mueller also talked about violence along the U.S.-Mexico border, where drug cartels and smugglers are responsible for a significant number of murders and other violence.

"To date, we have not had the same violence on this side of the border, that you have seen south of the border," said Director Mueller. "And we want to make certain that we do not see it and do everything we can to not only assure that it does not migrate to the United States, but also that we assist our Mexican colleagues to address it and disrupt and ultimately defeat that kind of violence."

The FBI director said his agency has made national security its top priority, but has not forgotten its crime fighting responsibilities.